THERMOELECTRIC-POWER OF TL-CA-BA-CU-O AND PR-TL-SR-CA-CU-O HIGH-TC SUPERCONDUCTORS

The resistance and the thermoelectric power of thallium based high Tc superconductors Tl-Ca-Ba-Cu-O and Pr-Tl-Sr-Ca-Cu-O have been measured in the temperature interval 77-300 K. The resistive behaviour of Tl-Ca-Ba-Cu-O is found to be metallic while that of Pr-Tl-Sr-Ca- Cu-O shows a mixed metallic and semiconductive behaviour. The thermoelectric power of both superconductors is positive throughout the temperature interval. The thermoelectric power of the Tl-Ca-Ba- Cu-O superconductor decreases linearly with increasing temperature above the superconducting transition temperature, Tc, below which it is zero. The thermoelectric power of the Pr-Tl-Sr-Ca-Cu-O sample shows a maximum near 180 K. The temperature dependence of the thermoelectric power of these samples, above Tc, is quite different than that observed for RBa2Cu3O7-x superconductors. © 1990.